Draft: Avoid libgweather 40 dependency
It'll be easier to do the libmutter-8-0 transition if we can decouple it from libgweather, and gnome-shell is written in a dynamic language, so we can easily avoid the dependency.
Untested, I need to build the whole cluster of packages described in https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=992870#12 before I can really try this (I'm avoiding pulling everything from experimental to get a more accurate picture of what it will be like when we do smaller transitions).